As a single crystal used as a semiconductor device substrate, there is, e.g., a silicon single crystal, and it is manufactured mainly based on a Czochralski (CZ) method. Although high integration of a semiconductor device advances in recent years, a problem of a grown-in defect which is introduced during growth of the silicon single crystal based on the CZ method is becoming serious with this high integration.
FIG. 2 is a distribution map of this grown-in defect.
As shown in FIG. 2, as the grown-in defect, there is a vacancy type defect caused due to a void, e.g., a FPD (Flow Pattern Defect) or a COP (Crystal Originated Particle) formed when a pulling rate F (mm/min) is relatively high, and a region where such a defect is present is called a V region. Further, an OSF (Oxidation Induced Stacking Fault) occurs with a reduction in the pulling rate F (mm/min). Furthermore, there is a defect having interstitial silicon agglomerated therein which is considered as a factor of a dislocation loop, e.g., an LSEPD (Large Secco Etch Pit Defect) or an LFPD (Large Flow Pattern Defect) which occurs at a low pulling rate F (mm/min), and a region where such a defect is present is called an I region.
It was recently discovered that an N region having no defect mentioned above is present between the V region where the FPD or the COP is present and the I region where the LSEPD or the LFPD is present outside an OSF ring. Further classifying this region, there are a vacancy type Nv region and an Ni region having a large amount of the interstitial silicon, and it is known that an amount of precipitated oxygen is large in the Nv region when thermal oxidation processing is performed and that oxygen precipitation hardly occurs in the Ni region.
Moreover, it is also known that a Cu deposition defect region having a defect detected by Cu deposition treatment is present in a part of the Nv region where oxygen precipitation is apt to occur after thermal oxidation processing.
Here, the Cu deposition treatment means processing of applying a electric potential to an oxide film formed on a wafer surface in a liquid in which a Cu ion is dissolved, and a current flows through a part where the oxide film is degraded and the Cu ion is precipitated as Cu. Additionally, it is known that a defect is present in this part where the oxide film is apt to be degraded. A defective part of a wafer subjected to the Cu deposition treatment can be analyzed under a collimated light or with the naked eye directly to evaluate its distribution or density, and it can be also confirmed based on microscopic observation using, e.g., a transmission electron microscope (TEM) or a scanning electron microscope (SEM).
In manufacture of a single crystal based on the CZ method, it is considered that an introduction amount of the above-explained grown-in defect is determined by a parameter called F/Gc (mm2/° C.·min). That is, adjusting the pulling rate F (mm/min) and a crystal temperature gradient Gc (° C./mm) near a solid-liquid interface of a central part of a crystal in such a manner that F/Gc (mm2/° C.·min) becomes constant enables pulling the single crystal with a desired defect region.
However, when a heat convection of a melt fluctuates and an intensive time fluctuation occurs in a temperature near the crystal solid-liquid interface during an operation of pulling the single crystal, the crystal temperature gradient Gc (° C./mm) near the solid-liquid interface of the central part of the crystal is not stabilized, and a ratio of the pulling rate F (mm/min) and the crystal temperature gradient Gc (° C./mm) near the solid-liquid interface of the central part of the crystal, i.e., F/Gc (mm2/° C.·min) varies with time. Further, when a temperature near the crystal solid-liquid interface fluctuates, a diameter of the single crystal to be pulled varies, the pulling rate F (mm/min) must be changed to suppress this fluctuation, and hence an amplitude range thereof is increased. Furthermore, when such a considerable time fluctuation occurs during growth of the large-diameter silicon single crystal having a diameter of 200 mm or above in particular, this becomes an obstacle to prevent a desired crystal defect distribution from being formed in the crystal growth direction.
For example, in case of controlling the pulling rate F (mm/min) in the N region having a narrow crystal manufacture margin to pull the silicon single crystal, when such a remarkable time fluctuation occurs in a temperature near the crystal solid-liquid interface, a region other than the N region, e.g., the V region, the OSF region, or the I region may be formed in the crystal growth direction in some cases. Moreover, a wafer sliced from such a crystal may have a problem of considerably degrading electrical characteristics. Therefore, a heat convection of the melt must be suppressed, and a desired crystal defect region must be uniformly formed in the crystal growth direction.
Thus, as a method of suppressing the heat convention of the melt and reducing a time fluctuation in a temperature of the single crystal to be pulled near the solid-liquid interface (a temperature near a melt surface), an MCZ method, e.g., a horizontal magnetic field application CZ method (an HMCZ method) of arranging magnetic field application devices each including an electromagnet, e.g., a superconducting magnet to face each other with a crucible sandwiched therebetween on the outer side of the heater for heating the crucible has been adopted.
For example, Japanese Patent Application Laid-open No. 2004-315289 discloses a method of setting a minimum magnetic field intensity in a melt to 2000 G or above, setting a maximum magnetic field intensity in the melt to 6000 G or below, and setting a maximum magnetic field gradient obtained by dividing a difference between the maximum and minimum magnetic field intensities by a distance thereof to 55 G/cm or below.
However, in order to manufacture a single crystal having a desired crystal defect formed in a growth direction with high productivity and a high production yield, these conventional manufacturing methods are insufficient, and further improvements are desired.
Additionally, in recent years, when a large-diameter silicon single crystal having a diameter of 300 mm is to be pulled with the N region, a growth rate must be increased, and productivity must be heightened. Thus, like the example of pulling a silicon single crystal having a diameter of 200 mm with the N region, a measure of reducing a length of a gas flow-guide cylinder to further rapidly perform cooling is taken. However, in a hot zone (an in-furnace structure) having such a rapid cooling structure, solidification disadvantageously very often occurs during crystal growth. Occurrence of such solidification is an obstacle for single-crystallization and leads to a reduction in a production yield of the N-region single crystal.